Teen's exposure to sexual content on the Web and its effects on their sexual health is an important but understudied public health issue. To address this issue, we propose an interdisciplinary collaboration between researchers at two academic institutions (Emory University and the University of Georgia Public Health Information Technology Laboratory) and Harris Interactive, a leading internet research company with a wealth of expertise. The proposed prospective study represents a unique opportunity to examine the effects of adolescents' exposure to Web pages that contain sexual content on the sexual health-related attitudes, beliefs and behaviors of a national probability sample of 865 teens (615 White and 250 African American male and female teens) 14-16 years of age. Specifically, the aims are: (1) to describe characteristics of teens who access Web pages that contain sexual health, sexually explicit and sexual related content; (2) to develop cross- sectional models examining the association between exposure to Web pages that contain sexual content and their sexual health- related knowledge, attitudes, beliefs, intentions and behaviors; (3) to prospectively examine the association between exposure to Web pages that contain sexual content and its effect on teens' sexual health-related knowledge, attitudes, beliefs, intentions and behavior over a 16-month follow-up period and; (4) to examine the effects of hypothesized moderators (i.e. parental monitoring, parental communication about sex, sociodemographics, other media exposures and exposure to sex education programs on the association between exposure to sexual content on the Web and hypothesized mediators and outcomes. To accomplish these aims, teens will be asked to complete Web-administered interviews (WAI) at baseline and at 4-,8-,12- and 16-month follow-ups. Teens will also be asked to download and install Web tracking software on their home computer which will provide an objective measure of Web exposure to sexual content. The Web pages that teens access will be automatically collected biweekly and the Web pages subjected to "robotic" coding. The "robot" Web coder is designed to electronically screen the HTML of tracked Web pages to identify those that contain sexual content. Web pages found to contain sexual content will be subjected to extensive content analysis by trained coders. Coders will use descriptive, contextual, and theoretically-informed categorization schemes to examine the characteristics of sexual content. Analyses will construct cross-sectional models to examine the relationship between teens' use of Web pages that contain sexually explicit, sexual health and sexually-related content, and their sexual health-related attitudes, beliefs, intentions and behaviors at 16-month follow-up, statistical analyses controlling for baseline assessments, will prospectively examine the relationship between teens' use of Web pages that contain sexually explicit, sexual health and sexually-related content and adolescents' sexual health-related attitudes, beliefs, intentions and behaviors. Given the controversy surrounding teens' exposure to sexual content on the Web, there is a compelling need to examine the impact of these exposures on teens' sexual health.